The optical properties of the coating samples were characterized using different techniques. Table REF  presents the measured values for the refractive index \(n\)  at the wavelengths of interest (1064 and 1550 nm) for current and future GW interferometers [1]}, [2]}, [3]}, [4]}. Optical absorption at 1064 nm was measured on RBTD single-layer samples and IBS multi-layer HR stacks. Light scattering at 1064 nm was measured on IBS multi-layer HR stacks. At 1550 nm, where only ellipsometric and photometric measurements were available, extinction values were smaller than the sensitivity of the instruments (\(k < 10^{-3}\) ). Measurements and their analyses are described below. A comparative summary is presented in Section REF , where correlations between oxygen concentration, density and refractive index are discussed.
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